The future ability to test theories of gravity with black-hole shadows

Abstract

The horizon-scale images of supermassive black holes (BHs) by the Event Horizon Telescope Collaboration (EHT) have provided new opportunities to test general relativity and other theories of gravity. In view of future projects, such as the next-generation Event Horizon Telescope (ngEHT) and the Black-Hole Explorer (BHEX), having the potential of enhancing our ability to probe extreme gravity, it is natural to ask: \textit{how much can two black-hole images differ?} To address this question and assess the ability of these projects to test theories of gravity with black-hole shadows, we use general-relativistic magnetohydrodynamic and radiative-transfer simulations to investigate the images of a wide class of accreting BHs deviating from the Kerr solution. By measuring the mismatch between images of different BHs we show that future missions will be able to distinguish a large class of BHs solutions from the Kerr solution when the mismatch in the images exceeds values between $2\%$ and $5\%$ depending on the image-comparison metric considered. These results indicate future horizon-scale imaging with percent-level image fidelity can place meaningful observational constraints on deviations from the Kerr metric and thereby test strong-field predictions of general relativity.

Published in Nature Astronomy

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Cited by in corpus (8)

• Ladder Symmetry: The Necessary and Sufficient Condition for Vanishing Love Numbers
• Shadows of naked singularities and superspinars related to the revisited Kerr-de Sitter spacetimes
• Observational distinguishability of the Kerr and Kerr-Hayward metrics to EHT
• Perturbative Renormalisation Group Improved Black Hole Solution and its Quasinormal Modes
• Relativistic Thermal Emission from Accretion Disks in Kerr-MOG Spacetimes
• Signatures of the Israel Junction II: Double Photon Rings in Slowly Rotating Kerr Spacetime with Thin Shell
• Spacetime of rotating black holes surrounded by massive scalar charges
• Universality of the Blandford-Znajek emission in stationary and axisymmetric spacetimes